Fuji Electric FRENIC-AQUA series, User Manual

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App. A Advantageous Use of Inverters (Notes on electrical noise)
A-7
App.
(3) Anti-noise devices
To reduce the noise propagated through the electrical circuits and the noise radiated from the main
circuit wiring to the air, a line filter and power supply transformer should be used (refer to Figure
A.10).
Line filters are available in these types--the simplified type such as a capacitive filter to be connected
in parallel to the power supply line and an inductive filter to be connected in series to the power
supply line and the orthodox type such as an LC filter to meet radio noise regulations. Use them
according to the targeted effect for reducing noise.
Power supply transformers include common insulated transformers, shielded transformers, and
noise-cutting transformers. These transformers have different effectiveness in blocking noise
propagation.
(a)
Capacitive filter
(b)
Inductive filter
(c)
LC filter
(zero-phase reactor)
Figure A.10 Various Filters and their Connection
(4) Noise prevention measures at the receiving side
It is important to strengthen the noise immunity of those electronic devices installed in the same
control panel as the inverter or located near an inverter. Line filters and shielded or twisted shielded
wires are used to block the penetration of noise in the signal lines of these devices. The following
treatments are also implemented.
1) Lower the circuit impedance by connecting capacitors or resistors to the input and output
terminals of the signal circuit in parallel.
2) Increase the circuit impedance for noise by inserting choke coils in series in the signal circuit or
passing signal lines through ferrite core beads. It is also effective to widen the signal base lines (0
V line) or grounding lines.
(5) Other
The level of generating/propagating noise will change with the carrier frequency of the inverter. The
higher the carrier frequency, the higher the noise level.
In an inverter whose carrier frequency can be changed, lowering the carrier frequency can reduce the
generation of electrical noise and result in a good balance with the audible noise of the motor under
driving conditions.